Cryotreatment devices and methods of forming conduction blocks

ABSTRACT

Cryotreatment devices and methods of ablating tissue within the body are disclosed. A cryotreatment device in accordance with an exemplary embodiment of the present invention includes an elongated member having one or more needle-like ablation tips configured to induce necrosis at a target site within the heart. A cooling fluid such as a cryogen may be injected through a lumen extending into the distal portion of the device. The ablation tips can be configured to pierce and ablate surrounding tissue, blocking electrical stimuli that can cause fibrillations or other arrhythmias of the heart. The device may also include means for controlling the transmural depth at which the ablation tips are inserted into the cardiac tissue. Methods of forming a contiguous line of conduction block in accordance with the present invention are also disclosed.

FIELD OF THE INVENTION

[0001] The present invention relates generally to medical devices forablating tissue at one or more target sites. More specifically, thepresent invention relates to cryotreatment devices and methods forinducing controlled necrosis of cardiac tissue within the heart.

BACKGROUND OF THE INVENTION

[0002] Cardiac arrhythmias such as atrial fibrillation, bradycardia,ventricular tachycardia, ventricle fibrillation, andWolff-Parkinson-White syndrome are common heart abnormalities that causestroke, myocardial infarction, and other thromboembolic events withinthe body. In patients with normal sinus rhythm, the heart iselectrically excited to beat in a synchronous and patterned manner,typically at a rate of 60 to 100 beats per minute (bpm). In contrast, inpatients with cardiac arrhythmia, abnormal regions of the cardiac tissuemay aberrantly conduct to adjacent tissue, causing the heart to beatirregularly. In ventricular tachycardia, for example, electrical signalsmay be errantly received in the lower heart chamber (i.e. the ventricle)instead of the right, upper chamber (i.e. the atria), causing the heartto beat rapidly. In atrial fibrillation, the most common type of cardiacarrhythmia, the upper chambers of the heart beat at an uncontrolled rateof 350 to 600 bpm, which results in a reduction of the pumping force ofthe heart. As a result of this reduced pumping force, blood in the heartchambers may become stagnant and pool, forming blood clots that candislodge within the body and cause stroke or other life threateningevents.

[0003] To treat cardiac arrhythmia, a number of therapeutic procedureshave been developed, including RF catheter ablation, chemicalcardioversion, percutaneous myocardial revascularization (PMR), andsuppression. Antiarrhythmic medications such as beta-blockers, calciumchannel blockers, anticoagulants, and DIGOXIN have also been usedsuccessfully to treat some forms of cardiac arrhythmia. More recenttrends have focused on the use of cryotreatment catheters to treatarrhythmias such as atrial fibrillation and ventricular tachycardia.Such devices provide a relatively non-invasive method of treatment incomparison to other surgical techniques.

[0004] In one such method, for example, a catheter loaded with acryogenic cooling fluid may used to cryogenically cool cardiac tissue atstrategic locations of the heart, such as the right and left atria, orthe pulmonary veins. The catheter can be used to induce necrosis at oneor more pre-mapped target sites within the heart to create conductionblocks within the aberrant electrical conduction pathways. In atrialfibrillation, for example, necrosis of one or more target sites withinthe atrial cardiac muscle tissue can be used to block the electricalsignals believed to cause and/or sustain the fibrillation.

[0005] In some techniques, the use of a cryotreatment device to form therequired conduction block may be ineffective since there is no adequatemeans to control the transmural depth of the lesion, or the distancebetween each lesion. To compensate for these shortcomings, manycryotreatment devices utilize relatively large catheter tips, whichdestroy more tissue than is necessary to form the conduction block andfurther reduce the already weakened pumping force of the heart. It istherefore desirable to have a cryotreatment device capable oftransmurally controlling the depth of each lesion and in a contiguousmanner.

SUMMARY OF THE INVENTION

[0006] The present invention relates generally to cryotreatment devicesand methods for reducing or eliminating arrhythmia by inducingcontrolled necrosis at one or more pre-mapped target sites within theheart. A cryotreatment device in accordance with an exemplary embodimentof the present invention may comprise an elongated member having aproximal portion, a distal portion, and one or more lumens therein influid communication with a cooling fluid adapted to cool the distalportion of the elongated member. The elongated member may include one ormore needle-like ablation tips configured to pierce and necrotizecardiac tissue within the heart, preventing the conduction of aberrantelectrical signals through the tissue to one or more relay sites ofarrthymogenic foci. The cryotreatment device may include one or morefeatures configured to form an array of ablations within the cardiactissue, forming a contiguous line of conduction block.

[0007] The ablation tips may be retractable within the elongated memberto control the penetration depth of the tips transmurally into thecardiac tissue. A pull cord operatively coupled to the ablation tip canbe used to retract the ablation tip from the cardiac tissue. Anultrasonic probe or other measuring device may also be provided tomeasure and control the insertion depth of the cryotreatment devicewithin the cardiac tissue.

[0008] A cryosurgical method in accordance with the present inventionmay comprise the steps of providing a cryotreatment device to a targetsite within the heart, and necrotizing one or more locations within thecardiac tissue to form a contiguous line of conduction block. A coolingfluid such as liquid nitrous oxide can be injected through an innerlumen extending to the distal portion of the cryotreatment device tocool the surrounding tissue adjacent the ablation tips.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 is an illustration of a cryotreatment device in accordancewith an exemplary embodiment of the present invention, wherein thedevice is shown inserted through the septal wall of the heart andadvanced to a target site at or near one or more relay points;

[0010]FIG. 2 is a partial cross-sectional view of the cryotreatmentdevice of FIG. 1;

[0011]FIG. 3 is a detailed view of the cryotreatment device of FIGS.1-2, wherein the device includes an ultrasonic probe adapted measure andcontrol the transmural depth of the device into the cardiac tissue;

[0012]FIG. 4 is another detailed view illustrating multiplecryotreatment devices coupled together using a coupling member;

[0013]FIG. 5 is a view of a cryotreatment device in accordance with anexemplary embodiment of the present invention, wherein the cryotreatmentdevice includes a linear array of ablation tips;

[0014]FIG. 6 is a partial cross-sectional view of a cryotreatment devicein accordance with an exemplary embodiment of the present invention,wherein the cryotreatment device includes several retractable cryogenictips configured to form a circumferential line of conduction blockwithin the heart; and

[0015]FIG. 7 is a partial cross-sectional view of a cryotreatment devicein accordance with another exemplary embodiment of the presentinvention, wherein the cryotreatment devices includes an enlarged distalportion with retractable ablation tips.

DETAILED DESCRIPTION OF THE INVENTION

[0016] The following description should be read with reference to thedrawings, in which like elements in different drawings are numbered inlike fashion. The drawings, which are not necessarily to scale, depictselected embodiments and are not intended to limit the scope of theinvention. Although examples of construction, dimensions, and materialsare illustrated for the various elements, those skilled in the art willrecognize that many of the examples provided have suitable alternativesthat may be utilized.

[0017]FIG. 1 is an illustrative view of a cryotreatment device 10 inaccordance with an exemplary embodiment of the present invention forinducing controlled necrosis at one or more pre-mapped target siteswithin the heart. A guide wire 12 inserted percutaneously into thefemoral or jugular veins is shown advanced through the septal wall 14and into the upper chambers 16,18 of a heart 20. Using knownmanipulation techniques in the art, guidewire 12 can be advanced to alocation distal a target site 22 determined to cause electricalinterference with one or more downstream arrythmogenic foci 24. A guidecatheter 26 sufficiently sized to receive cryotreatment device 10 can beused to advance the cryotreatment device 10 to a location at or near thetarget site 22.

[0018] Arrhythmias such as atrial flutter, atrial fibrillation andventricular tachycardia are typically caused when abnormal regions ofthe heart transmit aberrant electrical signals vis-à-vis arrythmogenicfoci. To treat such arrhythmias, a cryotreatment device in accordancewith the present invention can be inserted into cardiac tissue at apre-mapped target site and cooled to a temperature of about −40 to −100°C. to induce necrosis at one or more locations 28,30,32,34 within theheart, such as the pulmonary vein 36. The cryotreatment device can beinserted at the various locations 28,30,32,34 to form a line ofconduction block that prevents certain electrical signals from beingsent from the foci points 24. In necrotizing the cardiac tissue atseveral locations, thereby forming a line of conduction block in thepulmonary vein 36, the transmission of aberrant signals believed tocause the arrhythmia can be reduced or in some cases altogethereliminated.

[0019]FIG. 2 is a partial cross-sectional view of the cryotreatmentdevice 10 of FIG. 1, showing the distal portion 38 of the device 10 ingreater detail. In the exemplary embodiment of FIGS. 1-2, cryotreatmentdevice 10 comprises a multiple lumen catheter body 40 having an outershaft 42 configured to pierce and cool the cardiac tissue, and an innershaft 44 defining an inner lumen 46 in fluid communication with acooling fluid. The outer shaft 42 of catheter body 40 may have atransverse cross-sectional area that is substantially circular in shape,extending from a proximal end (not shown) located outside of thepatient's body to a transition region 48 on the catheter body 40. Attransition region 48, catheter body 40 tapers distally to a needle-likeablation tip 50 configured to pierce and contact cardiac tissue.

[0020] To cool the distal portion 38 of cryotreatment device 10 to asufficiently low temperature to induce necrosis when inserted intocardiac tissue, cryotreatment device 10 can be placed in fluidcommunication with a cooling fluid such as liquid nitrogen, nitrousoxide (N₂O), carbon dioxide (C₂O), chlorodifluoromethane,polydimethysiloxane, ethyl alcohol, chlorofluorocarbons (Freon), orother suitable fluid. The cooling fluid can be delivered in either aliquid or gas state through inner lumen 46, and injected into theannular space 52 between the outer and inner shafts 42,44 throughseveral apertures 54 disposed in the inner shaft 44. In one embodiment,for example, pressurized liquid nitrous oxide can be fluidly coupled tothe inner lumen 46 of catheter body 40, and ejected through severalapertures 54 disposed in the inner lumen 44. Using the Joule-Thompsoncooling effect, the apertures 54 are adapted to act as a throttlingelement (e.g. a throttling nozzle) for the cryogen, producingisenthalpic cooling as the fluid is expended from a relatively highpressure within the inner lumen 46 to a lower pressure as it enters theannular space 52. As the cryogenic fluid expands as it passes throughthe apertures 54, it transitions to a gas and impinges upon the interiorwall 56 of the outer shaft 42 cooling the distal portion 38 of thecatheter body 40. This temperature drop is then thermally transferredthrough the catheter body 40 and into the surrounding cardiac tissue 58,inducing necrosis at the target site 22. The cryogenic fluid issubsequently returned through annular lumen 52 to the proximal end ofthe device 10.

[0021] The number of apertures 54 can be varied to provide a desiredtemperature decrease to the distal portion 38 of the catheter body 40.The type of cryogen used and the pressure and/or volume at which thecryogen is delivered through the inner lumen 46 can also be selected toimpart a particular cooling characteristic to the device 10, as desired.In the exemplary embodiment of FIGS. 1-2, cryotreatment device 10includes several equidistantly spaced apertures 54 configured to provideuniform cooling through the distal portion 38 of the catheter body 40.It should be recognized, however, that the apertures 54 could be placedat any number of strategic locations, at either equidistant ornon-equidistant intervals, to direct the cryogenic fluid to a particularlocation within the device 10.

[0022] The outer and inner shafts 42,44 of cryotreatment device 10 maybe fabricated from materials having certain desirable flexibility andthermodynamic properties. For example, the outer and inner shafts 42,44may each be formed of a superelastic material such as nickel-titaniumalloy (Nitinol) to permit the cryotreatment device 10 to be insertedthrough relatively tortuous locations of the body without kinking. Othersuitable biocompatible materials such stainless steel or a polymer/metalcomposition may also be utilized, depending on the particularapplication.

[0023] Referring now to FIG. 3, methods of using cryotreatment device 10will now be described in the context of a cryosurgical procedure tonecrotize cardiac tissue 58 within a body lumen such as a pulmonary vein36. Cryotreatment device 10 can be inserted through a previouslypositioned guide catheter 26 and advanced to a pre-mapped target site 22within the heart believed to transmit aberrant electrical signals to oneor more relay points. As shown in FIG. 3, needle-like ablation tip 50 ofdevice 10 can be configured to pierce and contact the cardiac tissue 58of pulmonary vein 36, allowing the distal portion 38 of catheter body 40to be inserted into the cardiac tissue 58. A curved portion 60 on thecatheter body 40 may be adapted to orient the needle-like ablation tip50 in a direction substantially perpendicular to the tissue wall 58.

[0024] In one aspect of the present invention, cryotreatment device 10can be configured to measure and control the transmural depth at whichthe device is inserted into the cardiac tissue 58. Controlled insertionof the needle-tip ablation tip 50 into the cardiac tissue 58 preventsdistension of the vein 36 from occurring, and prevents the ablation ofcardiac tissue not necessary to form the conduction block. Controlledinsertion of the needle-like ablation tip 50 into the cardiac tissue 58also ensures that the cryotreatment device 10 is inserted at asufficient depth to form the desired conduction block.

[0025] An ultrasonic probe 62 or other measurement device may beutilized to measure the precise depth at which cryotreatment device 10is inserted into the cardiac tissue 58. The ultrasonic probe 62 can becoupled to catheter body 40 a predetermined distance from theneedle-like ablation tip 50, and engaged to acoustically measure thedepth at which the distal portion 38 is inserted into the cardiac tissue58. The ultrasonic probe 62 may be coupled to the catheter body 40, ormay be formed as a separate element that can be advanced along thecatheter body 40 and positioned proximal the cardiac tissue 58. In oneexemplary embodiment, the ultrasonic probe 62 may act as a guidingmember for the device 10, eliminating the need for a separate guidecatheter. Those of skill in the art will readily recognize that othersuitable devices for measuring the insertion depth of the cryotreatmentdevice 10 may be employed, including, for example, the use of an opticalprobe, acoustic reflective coatings, distal bipolar electrodes, orthrough the use radiographic techniques such as fluoroscopic markerbands.

[0026] In operation, a fluid controller or other similar device can becoupled to the proximal end of the cryotreatment device 10 and used toinject a controlled flow of cryogenic fluid (e.g. liquid N₂O) throughthe inner lumen 46. One or more temperature sensors (not shown) on thedistal portion 38 of catheter body 40 may also optionally be used tomonitor the temperature of the device 10 and adjust the flow rate viathe fluid controller, as necessary. An insulated sleeve 64 surroundingthe catheter body 40 may be utilized to thermally isolate the catheterbody 40 proximal the distal portion 38 to prevent ablating other areasof the body.

[0027] In certain embodiments, the cryotreatment device may include acoupling member configured to couple multiple ablation tips together inan array. As shown in FIG. 4, for example, a coupling member 66 can beused to connect multiple cryotreatment devices 10 together, forming alinear array of needle-like ablation tips 50 that, when thermally cooledvia a cryogenic fluid, create a line of contiguous conduction blockalong the cardiac tissue 58 at the target site 22. The coupling member66 can be configured to couple together any number of cryotreatmentdevices together in any desired array or pattern. The multiple coolingmembers 10 applied in a sequential cooling method will allow the lesionsto be made in a stitched like fashion to ensure contiguous connection ofall the lesions. The method of stitching is accomplished by moving oneneedle 50 while the other needle 50′ is anchored and froze into thetissue. The sequence of operation would be as follows:

[0028] 1. Insert two needles at start point and apply maximum freeze;

[0029] 2. Thaw the proximal needle and reduce temperature on distalneedle;

[0030] 3. Retract proximal needle and rotate around anchored distalneedle;

[0031] 4. Apply maximum cooling on both needles and repeat steps 2-4.

[0032]FIG. 5 is a view of a cryotreatment device 68 in accordance withanother exemplary embodiment of the present invention. Cryotreatment 68comprises a catheter body 70 having several linearly disposed ablationtips 72 along a distal portion 74 that, when placed into fluidcommunication with a cryogenic cooling fluid, are configured to form aline of conduction block within a target site of the heart. Eachablation tip 72 may be configured similar to tip 50 described above,having a needle-like shape configured to pierce and contact the cardiactissue when inserted. The number of needles 72 and lumens 76 may be thesame as shown, or may be as few as two needles 72 for any number oflumens 76 in the method previously described. An inner lumen 76 in fluidcommunication with a source of pressurized cryogen at or near theproximal end of the device 70 is configured to cool each ablation tip 72in a manner similar that described above with respect to cryotreatmentdevice 10. The cryotreatment device 70 may also optionally include anultrasonic probe or other measurement means (not shown) for measuringthe precise depth at which the ablations tips 72 are transmurallyinserted into the cardiac tissue. An insulation layer 78 surrounding thecatheter body 70 thermally insulates the body 70 from ablating otherareas of the body.

[0033] To form a line of conduction block within a target site of theheart, ablation tips 72 can be aligned with a portion of the cardiactissue believed to transfer the aberrant electrical signal(s) to one ormore downstream relay points, and inserted into the tissue at acontrolled depth. A pressurized cryogenic fluid can be delivered throughthe catheter body 70, causing the ablation tips 72 on the distal portion74 to undergo a temperature drop to a temperature of about −40 to −100°C., inducing necrosis in the surrounding cardiac tissue.

[0034] The destruction of more tissue than is necessary to form theconduction block may be mitigated through the use of a series of smallerablation tips. Moreover, the number, shape and arrangement of theablation tips may be varied in accordance with the particularapplication. In certain applications, for example, a cryotreatmentdevice in accordance with the present invention may be configured toform a circumferential line of conduction blocks at a target site withinthe heart.

[0035] In one exemplary embodiment shown in FIG. 6, a cryotreatmentdevice 80 in accordance with the present invention may include acatheter body 82 having several needle-like ablation tips 84 on distalend 86 that, when thermally cooled via a supplied source of cryogenicfluid, form a circumferential line of conduction block at a target sitewithin the heart (e.g. about a pulmonary vein). Cryotreatment device 80may comprise an outer shaft 88, and an inner shaft 90 disposed withinthe outer shaft 88. The inner shaft 90 can be configured to deliver apressurized source of cryogenic fluid such as liquid nitrogen or N₂Othrough aperture 92 towards the interior surface 94 of distal end 86,causing the interior surface 94 of the distal end 86 of catheter body 82to cool and conduct heat.

[0036] Each of the needle-like ablation tips 84 can be configured toretract through several openings 96 disposed on the distal end 86 of thecatheter body 82. A control wire 98 extending proximally from eachablation tip 84 to a location outside of the patient's body may be usedto retract each tip 84 through its respective opening 96, allowing theoperator to adjust the precise depth at which the tip 84 is inserted thecardiac tissue. A flange 100 coupled to each ablation tip 84 preventsthe tip 84 from being pulled proximally through opening 96 as controlwire 98 is retracted. As with any of the other embodiments describedherein, an ultrasonic probe or other suitable device can be utilized tomeasure and, if necessary, control the penetration depth of the ablationtips 84 within the tissue.

[0037] In use, cryotreatment device 80 can be advanced to a target sitewithin the heart, and, with the ablation tips 84 initially in a fullydeployed position, inserted into the cardiac tissue. Once the device 80is inserted into the tissue, the operator can retract the control wire98 proximally a distance, causing the ablation tips 84 to retract fromwithin the tissue a slight distance (e.g. 0.5-3.0 cm). An ultrasonicprobe or other suitable device may be used to measure the precise depthat which the ablation tips 84 are inserted into the cardiac tissue. Atthe desired depth, a pressurized flow of cryogen is then deliveredthrough the device, causing the distal end 86 of the device, includingthe ablation tips 84, to cool to a temperature of about −40 to −100° C.,forming a circumferential line of conduction block within the body.

[0038]FIG. 7 is a partial cross-sectional view of a cryotreatment device102 in accordance with another exemplary embodiment of the presentinvention. Cryotreatment device 102 comprises an outer shaft 104 havinga proximal portion (not shown), a distal portion 106, and an inner lumen108 in fluid communication with a cooling fluid such as liquid N₂O. Thedistal portion 106 of cryotreatment device 102 may be enlarged slightly,orienting several retractable needle-like ablation tips 110 in a widerradial array, permitting the formation of a circumferential line ofconduction block at larger target sites. A control wire 112 operativelycoupled to each ablation tip 110 can be utilized to adjust thetransmural depth of the tip 110 into the cardiac tissue. A flangedportion 114 on each ablation tip 110 prevents the operator from pullingthe ablation tip 110 proximally through the tip openings 116 on thedistal portion 106 of the outer shaft 104.

[0039] Having thus described the several embodiments of the presentinvention, those of skill in the art will readily appreciate that otherembodiments may be made and used which fall within the scope of theclaims attached hereto. Numerous advantages of the invention covered bythis document have been set forth in the foregoing description. It willbe understood that this disclosure is, in many respects, onlyillustrative. Changes may be made in details, particularly in matters ofshape, size and arrangement of parts without exceeding the scope of theinvention.

What is claimed is:
 1. A medical device for inducing controlled necrosisat a target site within the body, comprising: an elongated member havinga proximal portion, a distal portion, and at least one lumen therein influid communication with a cooling fluid; at least one ablation tipcoupled to the distal portion of said elongated member configured tocontact and ablate tissue; and means for controlling the transmuraldepth of said at least one ablation tip into the tissue.
 2. The medicaldevice of claim 1, wherein said elongated member includes an inner shaftdefining an intake lumen for said cooling fluid, and an outer shaftdefining an exhaust lumen for said cooling fluid.
 3. The medical deviceof claim 2, wherein said inner shaft includes at least one apertureconfigured to eject cooling fluid from said intake lumen into saidexhaust lumen.
 4. The medical device of claim 3, wherein said at leastone aperture comprises a throttling element.
 5. The medical device ofclaim 1, wherein said cooling fluid is a cryogen.
 6. The medical deviceof claim 5, wherein said cryogen is liquid nitrous oxide.
 7. The medicaldevice of claim 5, wherein said cryogen is selected from the groupconsisting of liquid nitrogen, carbon dioxide, chlorodifluoromethane,polydimethysiloxane, ethyl alcohol, and chlorofluorocarbons.
 8. Themedical device of claim 1, wherein said means for controlling thetransmural depth of said at least one ablation tip comprises anultrasonic probe.
 9. The medical device of claim 1, wherein said meansfor controlling the transmural depth of said at least one ablation tipcomprises a control wire.
 10. The medical device of claim 1, whereinsaid at least one ablation tip is a needle-like ablation tip.
 11. Themedical device of claim 1, wherein said at least one ablation tipcomprises a plurality of ablation tips.
 12. The medical device of claim11, wherein said plurality of ablation tips is retractable within thedistal portion of said elongated member.
 13. The medical device of claim11, wherein said plurality of ablation tips is linearly arranged alongthe distal portion of said elongated member.
 14. The medical device ofclaim 11, wherein said plurality of ablation tips is radially arrangedabout the distal portion of said elongated member.
 15. The medicaldevice of claim 11, wherein said plurality of ablation tips isconfigured to form a line of conduction block at said target site. 16.The medical device of claim 1, wherein the distal portion of saidelongated member is radially enlarged.
 17. The medical device of claim1, further comprising a guiding member configured to transport saidelongated member to the target site.
 18. A medical device for inducingcontrolled necrosis at a target site within the body, comprising: anelongated member having a proximal portion, a distal portion, and atleast one lumen therein in fluid communication with a cooling fluid; aplurality of ablation tips coupled to the distal portion of saidelongated member configured to contact and ablate tissue, said pluralityof ablation tips configured to form a line of conduction block at saidtarget site; and means for controlling the transmural depth of saidplurality of ablation tips into the tissue.
 19. The medical device ofclaim 18, wherein said elongated member includes an inner shaft definingan intake lumen for said cooling fluid, and an outer shaft defining anexhaust lumen for said cooling fluid.
 20. The medical device of claim19, wherein said inner shaft includes at least one aperture configuredto eject cooling fluid from said intake lumen into said exhaust lumen.21. The medical device of claim 20, wherein said at least one aperturecomprises a throttling element.
 22. The medical device of claim 18,wherein said cooling fluid is a cryogen.
 23. The medical device of claim22, wherein said cryogen is liquid nitrous oxide.
 24. The medical deviceof claim 22, wherein said cryogen is selected from the group consistingof liquid nitrogen, carbon dioxide, chlorodifluoromethane,polydimethysiloxane, ethyl alcohol, and chlorofluorocarbons.
 25. Themedical device of claim 18, wherein said means for controlling thetransmural depth of said plurality of ablation tips comprises anultrasonic probe.
 26. The medical device of claim 18, wherein said meansfor controlling the transmural depth of said at least one ablation tipcomprises a control wire.
 27. The medical device of claim 18, whereineach of said plurality of ablation tips are needle-like ablation tips.28. The medical device of claim 18, wherein each said plurality ofablation tips are retractable within the distal portion of saidelongated member.
 29. The medical device of claim 18, wherein saidplurality of ablation tips is linearly arranged along the distal portionof said elongated member.
 30. The medical device of claim 18, whereinsaid plurality of ablation tips is radially arranged about the distalportion of said elongated member.
 31. The medical device of claim 18,wherein the distal portion of said elongated member is radiallyenlarged.
 32. The medical device of claim 18, further comprising aguiding member configured to transport said elongated member to thetarget site.
 33. A medical device for inducing controlled necrosis at atarget site within the body, comprising: an elongated member having aproximal portion, a distal portion, and at least one lumen therein influid communication with a cooling fluid; at least one retractableablation tip coupled to the distal portion of said elongated member,said at least one retractable ablation tip being configured to contactand ablate tissue; and at least one control wire configured to retractsaid at least one retractable ablation tip within said tissue.
 34. Acryosurgical method for inducing controlled necrosis at a target sitewithin the heart, comprising the steps of: providing a cryotreatmentdevice having a proximal portion, a distal portion, and at least onelumen therein in fluid communication with a cryogenic fluid, the distalportion of said cryotreatment device including at least one ablation tipconfigured to contact and ablate tissue; advancing the cryotreatmentdevice to the target site and inserting said at least one ablation tipinto the tissue; controlling the transmural depth of said at least oneablation tip into the tissue; and injecting the cryogenic fluid throughsaid at least one lumen to the distal portion of the cryotreatmentdevice.
 35. The method of claim 34, wherein the step of controlling thetransmural depth of said at least one ablation tip into the tissuecomprises the steps of: providing an ultrasonic probe at or near thetarget site proximal said at least one ablation tip; and acousticallymeasuring the penetration depth of said at least one ablation tip intothe tissue.
 36. The method of claim 34, wherein the steps of creatingtransmural necrosis are accomplished by inserting one ablation tip intothe tissue to a controlled depth and anchoring by freezing to the tissuethen connectively placing the next.
 37. The method of claim 34, whereinsaid at least one ablation tip comprises a plurality of ablation tipsconfigured to form a line of conduction block at the target site. 38.The method of claim 34, wherein the step of injecting the cryogenicfluid through said at least one lumen to the distal portion of thecryotreatment device comprises the steps of: supplying cryogenic fluidthrough an intake lumen to the distal portion of the cryotreatmentdevice; and ejecting the cryogenic fluid through one or more aperturesinto an exhaust lumen, said one or more apertures configured to cool thecryogenic fluid.
 39. A cryosurgical method for inducing controllednecrosis at a target site within the heart, comprising the steps of:providing a cryotreatment device having a proximal portion, a distalportion, and at least one lumen therein in fluid communication with acryogenic fluid, the distal portion of said cryotreatment deviceincluding a plurality of linearly-disposed ablation tips configured tocontact and ablate tissue; advancing the cryotreatment device to thetarget site; inserting said plurality of ablation tips into the tissue;controlling the transmural depth of said plurality of ablation tips intothe tissue; and injecting the cryogenic fluid through said at least onelumen to the distal portion of the cryotreatment device to form a lineof conduction block at the target site.
 40. The method of claim 39,wherein the step of controlling the transmural depth of said pluralityof ablation tips into the tissue comprises the steps of: providing anultrasonic probe at or near the target site proximal said plurality ofablation tips; and acoustically measuring the penetration depth of saidplurality of ablation tips into the tissue.
 41. The method of claim 39,wherein the step of injecting the cryogenic fluid through said at leastone lumen to the distal portion of the cryotreatment device comprisesthe steps of: supplying cryogenic fluid through an intake lumen to thedistal portion of the cryotreatment device; and ejecting the cryogenicfluid through one or more apertures into an exhaust lumen, said one ormore apertures configured to cool the cryogenic fluid.
 42. Acryosurgical method for inducing controlled necrosis at a target sitewithin the heart, comprising the steps of: providing a cryotreatmentdevice having a proximal portion, a distal portion, and at least onelumen therein in fluid communication with a cryogenic fluid, the distalportion of said cryotreatment device including a plurality ofradially-disposed ablation tips configured to contact and ablate tissue;advancing the cryotreatment device to the target site; inserting saidplurality of ablation tips into the tissue; controlling the transmuraldepth of said plurality of ablation tips into the tissue; and injectingthe cryogenic fluid through said at least one lumen to the distalportion of the cryotreatment device to form a circumferential line ofconduction block at the target site.
 43. A cryosurgical method forinducing controlled necrosis at a target site within the heart,comprising the steps of: providing a cryotreatment device having aproximal portion, a distal portion, and at least one lumen therein influid communication with a cryogenic fluid, the distal portion of saidcryotreatment device including a plurality of ablation tips configuredto contact and ablate tissue; advancing the cryotreatment device along aguiding member to the target site and inserting said plurality ofablation tips into the tissue; providing an ultrasonic probe at or nearthe target site proximal said plurality of ablation tips andacoustically measuring the penetration depth of said plurality ofablation tips into the tissue; and injecting the cryogenic fluid throughsaid at least one lumen to the distal portion of the cryotreatmentdevice, thereby forming a conduction block within the target siteblocking electrical signals to one or more relay points within theheart.
 44. The method of claim 43, wherein said guiding member comprisesa guide catheter disposed along a guidewire.